Spiral Flows in Cool-Core Galaxy Clusters

Keshet, Uri

doi:10.1088/0004-637x/753/2/120

Cited by 20 publications

(28 citation statements)

References 64 publications

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“…Such bubble entrainment was previously suggested by Keshet (2012). Future numerical simulations, that include both jet inflated bubbles and sloshing, will test this possible interpretation.…”

Section: Amplified Magnetic Fields Underneath the Cold Frontsupporting

confidence: 61%

Deep Chandra observation and numerical studies of the nearest cluster cold front in the sky

Werner

ZuHone

Zhuravleva

et al. 2015

Monthly Notices of the Royal Astronomical Society

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We present the results of a very deep (500 ks) Chandra observation, along with tailored numerical simulations, of the nearest, best resolved cluster cold front in the sky, which lies 90 kpc (19 ) to the northwest of M 87. The northern part of the front appears the sharpest, with a width smaller than 2.5 kpc (1.5 Coulomb mean free paths; at 99 per cent confidence). Everywhere along the front, the temperature discontinuity is narrower than 4-8 kpc and the metallicity gradient is narrower than 6 kpc, indicating that diffusion, conduction and mixing are suppressed across the interface. Such transport processes can be naturally suppressed by magnetic fields aligned with the cold front. Interestingly, comparison to magnetohydrodynamic simulations indicates that in order to maintain the observed sharp density and temperature discontinuities, conduction must also be suppressed along the magnetic field lines. However, the northwestern part of the cold front is observed to have a nonzero width. While other explanations are possible, the broadening is consistent with the presence of Kelvin-Helmholtz instabilities (KHI) on length scales of a few kpc. Based on comparison with simulations, the presence of KHI would imply that the effective viscosity of the intra-cluster medium is suppressed by more than an order of magnitude with respect to the isotropic Spitzer-like temperature dependent viscosity. Underneath the cold front, we observe quasi-linear features that are ∼ 10 per cent brighter than the surrounding gas and are separated by ∼ 15 kpc from each other in projection.Comparison to tailored numerical simulations suggests that the observed phenomena may be due to the amplification of magnetic fields by gas sloshing in wide layers below the cold front, where the magnetic pressure reaches ∼ 5-10 per cent of the thermal pressure, reducing the gas density between the bright features.

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Section: Amplified Magnetic Fields Underneath the Cold Frontsupporting

confidence: 61%

Deep Chandra observation and numerical studies of the nearest cluster cold front in the sky

Werner

ZuHone

Zhuravleva

et al. 2015

Monthly Notices of the Royal Astronomical Society

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“…A realistic spiral flow simulation, incorporating the physical processes outlined above, would directly test our approximation of two-phases composing the spiral, and gauge the simplified power-law scalings we derive. Simulations and observations would also test additional predictions of the model, such as the presence of a convective zone, a CF intermittency, and entrained radio bubbles (Keshet 2012). The role of the spiral flow in regulating the universal profile will be ruled out if Figure 7.…”

Section: Discussionmentioning

confidence: 99%

A Dynamically Driven, Universal Thermal Profile of Galaxy Groups and Clusters

Reiss

Keshet

2015

ApJ

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Large scale structures such as groups and clusters of galaxies show a universal, nearly linear entropy radial profile K(r). Using 16 deprojected clusters and 12 deprojected groups from the literature, we find that K ∝ r 0.96±0.01 , consistent with the mean power-law index (0.9-1.1) of previous studies. A similarly good fit is given by a τ ∝ r 0.72±0.01 ratio between cooling and free-fall times. Both profiles slightly flatten at small radii, as τ becomes of order unity. The entropy profile is usually attributed to self-similar shock accretion (shown to be inconsistent with the data), to non-standard heat conduction, or to turbulent heating. We argue that a dynamical mechanism is needed to sustain such a universal profile, oblivious to the temperature peak at the edge of the core and to the virial shock at the outskirts, and robust to the presence of ongoing cooling, merger, and active galactic nucleus activity. In particular, we show that such a profile can be naturally obtained in a spiral flow, which is likely to underlie most galaxy aggregates according to the ubiquitous spiral patterns and cold fronts observed. Generalizing a two-phase spiral flow model out to the virial radius surprisingly reproduces the thermal profile. A generalized Schwarzschild criterion indicates that observed spiral patterns must involve a convective layer, which may regulate the thermal profile.

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“…Simulations also show that there is a general radial expansion of the cold fronts away from the cluster potential minimum (Roediger et al 2011). Keshet (2012) demonstrated that such expanding, spiral flows must have a "bulging" cylindrical or "open barrel" shape as seen from lines of sight parallel to the sloshing plane. viscid simulation at an epoch t ∼ 1.6 Gyr past the core passage.…”

Section: Velocity Moment Mapsmentioning

confidence: 90%

Simulating Astro-H Observations of Sloshing Gas Motions in the Cores of Galaxy Clusters

ZuHone

Miller

Simionescu

et al. 2016

ApJ

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Astro-H will be the first X-ray observatory to employ a high-resolution microcalorimeter, capable of measuring the shift and width of individual spectral lines to the precision necessary for estimating the velocity of the diffuse plasma in galaxy clusters. This new capability is expected to bring significant progress in understanding the dynamics, and therefore the physics, of the intracluster medium. However, because this plasma is optically thin, projection effects will be an important complicating factor in interpreting future Astro-H measurements. To study these effects in detail, we performed an analysis of the velocity field from simulations of a galaxy cluster experiencing gas sloshing, and generated synthetic X-ray spectra, convolved with model Astro-H Soft X-ray Spectrometer (SXS) responses. We find that the sloshing motions produce velocity signatures that will be observable by Astro-H in nearby clusters: the shifting of the line centroid produced by the fast-moving cold gas underneath the front surface, and line broadening produced by the smooth variation of this motion along the line of sight. The line shapes arising from inviscid or strongly viscous simulations are very similar, indicating that placing constraints on the gas viscosity from these measurements will be difficult. Our spectroscopic analysis demonstrates that, for adequate exposures, Astro-H will be able to recover the first two moments of the velocity distribution of these motions accurately, and in some cases multiple velocity components may be discerned. The simulations also confirm the importance of accurate treatment of PSF scattering in the interpretation of Astro-H/SXS spectra of cluster plasmas.

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Spiral Flows in Cool-Core Galaxy Clusters

Cited by 20 publications

References 64 publications

Deep Chandra observation and numerical studies of the nearest cluster cold front in the sky

Deep Chandra observation and numerical studies of the nearest cluster cold front in the sky

A Dynamically Driven, Universal Thermal Profile of Galaxy Groups and Clusters

Simulating Astro-H Observations of Sloshing Gas Motions in the Cores of Galaxy Clusters

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